The disclosure of Japanese Patent Application No. HEI 11-002993 filed on Jan. 8, 1999 including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
The present invention relates to the method for chamfering a periphery of an opening of an inclined hole formed in a member, more specifically relates to the method for chamfering a periphery of an opening of an inclined hole having double angles (i.e. an inclined hole that is non-parallel to two or more reference axes of the member).
2. Description of the Related Art
Normally, when chamfering is performed on the inclined hole formed on a curved surface of the member, a shape of a chamfer varies according to a surface shape of the member, an angle of the hole, etc., and hence it is difficult to define its shape uniquely. Taking an oil hole of a crankshaft for example, a problem arising out of this fact will be explained below.
FIG. 16 and FIG. 17 are diagrams showing a crankshaft 1. Generally, an oil hole 3 for supplying lubricating oil is formed in a pin 2 of the crankshaft 1. This oil hole 3 pierces the pin 2 and an arm 6, running straight down to an oil hole 5 formed in a journal 4, and communicates with a middle part of the oil hole 5. FIG. 18A is an enlarged diagram showing only the pin 2 of the crankshaft 1. Also, FIG. 18B is a sectional view of the pin 2 being cut at connecting portion between the arm 6. As shown in the figures, if a shaft center of the pin 2 is set to be in the X axis direction and both the Y and Z axes are set so as to cross perpendicular to the X axis and also to each other, the oil hole 3 is non-parallel to the X axis and does not pass through an intersection of the Y axis and the Z axis (that is, the oil hole 3 is a hole non-parallel to radial direction of the pin). As described above, an inclined hole that is not parallel to two or more reference axes of the member is referred to as xe2x80x9can inclined hole having double anglesxe2x80x9d in the present description.
By the way, in a manufacturing process of the crankshaft 1, the crank shaft 1 is required to go through quenching to improve its mechanical characteristic. Typically, a quenching process is performed after the oil hole 3 is drilled. In this process, stress concentration occurs at the opening of the oil hole 3 and therefore problems such as a crack are apt to occur. In view of this, to prevent the occurrence of a crack, it is necessary to chamfer the opening of the oil hole 3 beforehand. A chamfer at the opening of the oil hole 3 is also necessary after the crankshaft 1 has been incorporated in an engine in order to improve the circulation of the lubricating oil etc. Therefore, if a chamfered portion of the oil hole 3 which was drilled before the quenching remains with necessary dimensions even when a grinding process after quenching has been completed, re-chamfering becomes unnecessary, hence being convenient.
Since the oil hole 3 is the inclined hole having double angles as described above, it appears as an opening of an elliptical shape on a cylindrical surface of the pin 2. If the chamfering operation is performed on this opening of the oil hole 3 with a shaft center of a chamfering drill brought in line with a central axis CL of the oil hole 3, a uniform chamfering all around the periphery of the opening cannot be done, rather the chamfer width becomes non-uniform, increasing or decreasing along the periphery all around (the term xe2x80x9cuniformxe2x80x9d means that xe2x80x9cthe chamfer width is uniform when viewed in an arbitrary directionxe2x80x9d). Also, in laid-open Publication No. HEI 6-55319 of unexamined Japanese Patent Application, a technique is disclosed that a uniform chamfering is realized by adopting a method wherein the shaft center of the chamfering drill is brought in line with the central axis CL of the oil hole 3 and the shaft center of the drill is translated in parallel with respect to the central axis CL of the oil hole 3, by a prescribed amount. However, with the technique in concern, the chamfer width cannot be made uniform when viewed in an arbitrary direction. To prevent the occurrence of a crack in the quenching process, a minimum required chamfering width needs to be secured. Also, to retain the chamfered portion having necessary dimensions after the grinding process, a sufficient chamfer width must be secured in the chamfering operation before the quenching. Accordingly, in the conventional method, the chamfering drill is inserted into the member to a deeper position so that the chamfer width at a position where the chamfer width is smallest among non-uniform chamfer widths all around the periphery can be processed so as to have necessary chamfer dimension or more.
As described above, the conventional processing method involves chamfering in unnecessary widths as a whole, and this constraint becomes a cause which hinders realization of a small-sized, lightweight engine. This is because it is necessary to secure xe2x80x9ca land widthxe2x80x9d for the pin 2 of the crankshaft 1. Here, the land width is a length of the pin 2 along the X axis necessary to secure an area of an oil film formed between the surface of the pin 2 and a crank pin metal (not shown in the figure). A land width greater than a certain value is necessary in preventing the occurrence of seizure etc. However, the oil hole 3 and chamfering portion thereof cannot be included into the land width. Therefore, a necessary dimension of the pin 2 along the X axis comes to the sum of a necessary land width, a diameter of the oil hole 3, and the chamfer dimension.
That is, as long as the conventional method for chamfering is employed, a sufficient value must be secured as the chamfer dimension from a design phase, which resulted in making the dimension of the pin 2 along the X axis longer. Then this method makes a total length of the crankshaft 1 increase, which results in an increase of a total length of an engine and augmentation of a weight of the engine.
As can be understood from the above, if controlling the chamfer width, namely chamfering a hole uniformly all around periphery thereof and the like, is possible, even for the oil hole 3 which is the inclined hole having double angles, it becomes unnecessary to secure chamfer dimension in excess, which will then bring about a large advantage in designing the engine, such as enabling reduction of the total length thereof etc.
The present invention has been made in view of the above-mentioned problem. Its object is to provide a method for chamfering the periphery of the opening of the inclined hole formed in the member, more specifically to provide a method for chamfering the inclined hole having double angles which can control the chamfer width on the periphery of the opening of the inclined hole.
A first embodiment according to the present invention for solving the above-mentioned problem is a method for chamfering the periphery of the opening of the inclined hole formed in the member, characterized in that an approach angle of the chamfering tool is calculated on a plane which passes through both the central axis of the above-described inclined hole and chamfering points and then chamfering is performed based on the calculation result.
In the present invention, when chamfering the periphery of the opening of the above-described inclined hole, relationships between a cross section of the above-described inclined hole as well as a surface shape of the above-described member and a tip end of the above-described chamfering tool are examined. Since a shape of the tip end of the chamfering tool is already known, a chamfer shape at the chamfering points can be determined geometrically on the above-described plane. Consequently, if the approach angle of the chamfering tool on the above-described plane is made to change, the chamfer shape can be directly controlled at the chamfering points, so that a necessary chamfer shape can be surely obtained.
Further, a second embodiment according to the present invention is a method for chamfering the periphery of the opening of the inclined hole having double angles formed in the member, comprising the steps of: modeling the above-described member and inclined hole thereof in a three-dimensional coordinate system; cutting off the above-described model with the plane which passes through both the central axis of the above-described inclined hole and the chamfering points; thereby recognizing the above-described member and the above-described inclined hole in two dimensions; determining the approach angle of the chamfering tool to obtain the desired chamfer shape by the use of the cross section of the inclined hole and a surface shape of the above-described member both of which have been projected on the two-dimensional plane; and performing the chamfering operation based on a result of the determination.
According to this construction of procedures, even an inclined hole having double angles can be recognized in two dimensions regarding the surface shape of the above-described member and the above-described inclined hole by cutting off the above-described model with the plane which passes through both the central axis of the above-described inclined hole and the chamfering points. Further, a shape of the tip end of the chamfering tool is overlapped to the cross section of the inclined hole and the surface shape of the above-described member both of which have been projected on the two-dimensional plane. Since the shape of the tip end of the chamfering tool is already known, the chamfer shape at the chamfering points can be determined geometrically. Consequently, if the approach angle of the chamfering tool is made to change on the above-described plane, the chamfer width at a point where control thereof is required can be directly controlled. By the way, since, in an initial phase of each of the above-mentioned processes, the above-described member and inclined hole thereof are modeled in a three-dimensional coordinate system and the model is cut, the position of the above-described plane can be grasped in the above-described three-dimensional coordinates. Therefore, the approach angle of the chamfering tool that is under examination on the above-described plane can also be grasped in the above-described three-dimensional coordinates.
Also, in the present invention, the approach angle of the above-described chamfering tool may be calculated based on a ratio concerning the chamfer widths at the chamfering points that appear on the above-described plane.
By the way, since the above-described plane passes through the central axis of the inclined hole, the two chamfering points, each of which is located at a symmetrical position to each other with reference to the central axis of the inclined hole, appear on the above-described plane. So, two chamfer widths at these two chamfering points are compared to find the ratio concerning the widths, and then the approach angle of the chamfering tool is calculated based on the ratio. To be concrete, the approach angle of the chamfering tool at which the ratio concerning the chamfer widths at the two chamfering points described above becomes a desired value is determined geometrically, and chamfering is performed based on the approach angle. The above-described chamfer widths are used to designate chamfer widths when viewed in an arbitrary direction on the above-described plane and the direction of view may be determined according to need. That is, according to the present invention, a chamfer width when viewed in an arbitrary direction can be controlled at an arbitrary point where controlling of a chamfer width is required.
Further, in the present invention, the approach angle of the above-described chamfering tool may be set so as to meet an equation a=b, where a denotes a chamfer width at one of the two chamfering points appearing on the above-described plane and b denotes a chamfer width at the other chamfering point.
This means that chamfer widths can be made uniform at the chamfering points by setting the approach angle of the above-described chamfering tool so that two chamfer widths at the two chamfering points, which are located at symmetrical positions to each other with respect to the central axis of the inclined hole, become identical.
Further, in the present invention, the above-described member may be a shaft-like member. Desired chamfer widths are processed at the chamfering points of the inclined hole formed on the cylindrical surface of the shaft-like member.